Method of concentrating radioactive waste

ABSTRACT

A METHOD OF CONCENTRATING AQUEOUS SOLUTONS AND SUSPENSIONS OF RADIOACTIVE WASTE BY THICKENING AND DRYING PROCESSES. THE METHOD IS CHARACTERIZED IN THAT THE CONCENTRATE IS DRIED ON HEATED ROLLERS, WHEREBY A POLYELECTROLYTE IS ADDED, IN A KNOWN MANNER, FOR THE PURPOSE OF ADJUSTING AN APPROPRIATE VISCOSITY. BONE GLUE IS ADDED, IN ORDER TO PREVENT FORMATION OF DUST AND AS AN EMBEDDING MASS. THE ROLLER PRODUCT IS SUBSEQUENTLY COMPRESSED INTO SOLID BODIES.

United States Patent Oifice 3,679,595 Patented July 25, 1972 METHOD OF CONCENIgJABTING RADIOACTIVE Walter Diillgast, Erlangen, Germany, assignor to Siemens Aktiengesellschaft, Berlin and Munich, Germany No Drawing. Filed June 19, 1969, Ser. No. 834,866 Claims priority, application Germany, June 29, 1968, P 17 64 586.2 Int. Cl. C09k 3/00, 3/22 US. Cl. 252301.1 W 3 Claims ABSTRACT OF THE DISCLOSURE A method of concentrating aqueous solutions and suspensions of radioactive waste by thickening and drying processes. The method is characterized in that the concentrate is dried on heated rollers, whereby a polyelectrolyte is added, in a known manner, for the purpose of adjusting an appropriate viscosity. Bone glue is added, in order to prevent formation of dust and as an embedding mass. The rolled product is subsequently compressed into solid bodies.

The present invention relates to a method for concentrating aqueous solutions and suspensions of radioactive waste by thickening and drying. It is known to concentrate such liquids up to a solid content to 10 to 15%. This concentrate is bound by being mixed with cement or hot bitumen or asphalt and stored in standard 200 liter barrels, in collecting places. The content of such a storage barrel containing radioactive waste, is virtually not determined at the barrel wall by the highly permeable radiation of 200 mr./h., but by the applied storage technique. The bitumizing is associated with a very large expenditure, with regard to machinery, and permits the embedding of a maximum of 60% by weight of solid materials. During a simple cementing process, a maximum of only by weight of solid materials can be included.

Thus is posed the problem of finding a method which would permit the embedding of greater weight shares of solid materials so that the elimination of radioactive wastes becomes simpler, less dangerous and more economical. This object is realized by the present invention through the. fact that the concentrate is dried on heated rollers, accompanied by the known process of adding polyelectrolyte, such as polyacrylamide to adjust the appropriate viscosity, while formation of dust is prevented by the addition of bone glue as an embedding mass and subsequently the rolled mass is compressed to form solid bodies.

This method makes it possible to bind up to 70% by weight of solid substances. A conventional bone glue or gelatin is added to the concentrate, produced in the customary manner. There is no danger that the bone glue may precipitate, since pH values of 2-3 must be adjusted for the evaporation. A very important advantage of using bone glue consists in the fact that the latter is viscous at temperatures required for drying, so that dust will be reliably prevented. Another advantage associated with bone glue is the fact that the latter has great radiation resistance, being an albumen substance. Its softening point depends on its water content and can therefore be simply adjusted as to be compressible for the purpose of reducing the volume. It binds 12 to 14% water, similarly to water of crystallization. When the actual value deviates therefrom, the water is bound or free.

All necessary processing temperatures are below 140 C., which is a good range for technical use. During a heating process above 130 C. the water content decreases below 8%. When this point is reached, the bone glue becomes water insoluble which is of great importance for storing radioactive wastes in underground storage places, such as old mine pits.

Due to the good heat transfer, the drying of the concentrate is preferably carried out on a rolled dryer. To this end, and in accordance with a known method, the viscosity must be so altered, by admixing polyacrylamide, that an adequate film can be obtained on the drying roller. The addition of bone glue or of another organic glue, such as hide glue, prevents, as previously indicated, the forming of dust. The residual moisture which is desired for the compression process that forms solid bodies, can be obtained directly on the roller or during a subsequent drying process.

An example resulting from practical application, will show the advantages of this method in greater detail:

2 to 3 kg. dry substance are contained in 1 cubic meter non-concentrated waste water. Evaporation increases the amount of solid substance to approximately 12%, that is one cubic meter concentrate contains approximately kg. dry substance. To increase the toughness of the concentrate 10 g, polyacrylamide are added for each 100 liter and also dry bone glue is added in an amount of approximately 2% by weight of the concentrate and is dissolved. This liquid is now dried on a roller, heated, e.g. by induction and having a surface temperature of about to C. The resulting dry substance layer is removed by an adjustable knife which is about 0.05 mm. from the roller and filled into a barrel. The volume of the dry substance is further reduced by means of pressing. In this manner, the solid substance from 60 to 90 cubic meters of waste water can be placed into a 200 liter barrel.

These explanations show that the heretofore practiced binding of radioactive wastes in bitumen or in a cement mixture can be replaced by a much simpler and cheaper bone glue binding which, in addition, affords the great advantage of being dust free which is of particular importance with respect to the radioactivity of the wastes.

It is expedient when filling these solidified wastes into transport containers, to line the latter with a material which would partly absorb the radiation, so that the permissible dose of radiation will not be exceeded at the outer surface of the barrels, which fact cannot be ensured for wastes of higher radioactivity in view of binding of up to 70% by weight of solids which is feasible with the method of the invention.

I claim:

1. A process for concentrating aqueous solutions and suspensions of radioactive waste by thickening and drying which comprises adding a polyelectrolyte to adjust the viscosity, adding bone glue to prevent formation of dust and to form an embedding mass, drying the concentrate on heated rollers and compressing the rolled product into solid bodies.

2. The process of claim 1, wherein polyacrylamide is the polyelectrolyte.

3. The process of claim 1, wherein the rolled mass is heated to above 130 C. which makes it insoluble and reduces the water content below 8%.

References Cited Alberti: German application 1,199,414, printed Aug. 26, 1965 (KI 21g2l/33), 3 pp. spec.

LELAND A. SEBASTIAN, Primary Examiner 

